Cocaine abuse and vulnerability to dependence and relapse during abstinence is one of the great challenges on the public health agenda of the United States, with an enormous cost in human tragedy as well as in public health and safety. An improved understanding of the mechanisms underlying cocaine dependence and relapse is necessary to generate new pharmacological and behavioral strategies for treatment. Vulnerability to environmental cues previously associated with cocaine-taking behavior (cue reactivity) is thought to promote cycles of dependence and relapse, a neural process that involves the mesocorticoaccumbens dopamine (DA) pathway which arises in the ventral tegmental area (VTA). A considerable literature has implicated the VTA in the brain and behavioral response to cocaine-associated cues, although our knowledge of the neurochemical afferents to the VTA that control cue reactivity is limited. Serotonin (5-HT) terminals densely innervate VTA neurons which express the 5-HT2C receptor (5-HT2CR); activation of the 5-HT2CR exerts an overall inhibitory influence over the function of the VTA and related cocaine-mediated behaviors. Thus, the 5-HT2CR in the VTA provides functional tone over behavior; however, the role for VTA 5-HT2CR signaling in cue reactivity has yet to be explored. Our long term goal is to elucidate the contribution of 5-HT2CR regulation to cue reactivity as a means to identify novel pharmacological approaches for treating cocaine addiction. The objective of this proposal is to employ innovative and complementary behavioral, biochemical and pharmacological approaches to identify differences in the status of 5-HT2CR function that contribute to expression of the high vs. low cue reactivity phenotype and to manipulate this system to test specific hypotheses regarding a role for the 5-HT2CR in cocaine-seeking behavior. The following aims will test our the overarching hypothesis that malfunctional 5- HT2CR signal transduction in the VTA emerges during forced abstinence from cocaine self-administration to drive the high cue reactivity phenotype: (1) interrogate VTA 5-HT2CR localization and signal transduction in cue reactivity phenotypes; (2) identify functional sensitivity of VTA 5-HT2CR signal transduction in cue reactivity phenotypes; (3) assess the impact of VTA 5-HT2CR knockdown on cue reactivity.. Upon completion, the applicant will acquire training and knowledge in new concepts and methodologies including the neurobiology of cue reactivity and psychostimulant addiction, the experimental design and analyses of behavioral pharmacology, neurochemical, and virally-mediated gene manipulations, and translational neuropharmacology principles. These innovative, translational studies will be the first to systematically explore the functional contribution of VTA 5-HT2CR in cue reactivity following an extended period of abstinence. The neurobiological understanding of how 5-HT2CR homeostasis within the mesocorticoaccumbens circuit contributes to the dynamic events underlying persistent maladaptive behaviors associated with cocaine dependence will allow for the exploration of new molecular entities to suppress cue reactivity and minimize relapse in cocaine addiction.